As described in particular in Patents N.degree.s FR-A-2 443 853, FR-A-2 387 062, and AT-368 368, cross-country ski boots are already well known in which the soles, made of a molded plastic material, have hollow and/or raised parts intended to cooperate with corresponding raised and/or hollow parts on the upper surface of a cross-country ski. One especially well-known ski boot has a sole equipped with a central longitudinal groove which cooperates with a longitudinal rib on the upper surface of the ski in order to provide lateral control of the boot when the skier's foot is spread out flat on the ski. By virtue of their design, the soles of cross-country boots of this kind make contact with the raised and/or hollow parts of the cross-country ski in circumscribed areas where the frictional forces are concentrated, and, in these circumscribed areas, the soles show a substantially-reduced resistance to wear. This wearing phenomenon is especially pronounced in the area providing support for the heel, which is alternately raised and lowered during cross-country skiing, and which thus comes into periodic contact with the ski.